Methods for differentiating plasma- derived protein from recombinant protein in a sample

ABSTRACT

The present invention relates, in general, to methods for detecting and quantitating plasma-derived protein and recombinant protein in a sample based on the difference in protein glycosylation, when the plasma protein and the recombinant protein are essentially the same protein.

This application claims the priority benefit of U.S. ProvisionalApplication No. 61/017,091, filed Dec. 27, 2007, herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

The invention relates, in general, to methods to differentiate andquantitate plasma derived protein and recombinant protein in a sampleusing a glycosylation-specific binding assay.

BACKGROUND OF THE INVENTION

Glycosylation is the process of, or the result of, addition ofcarbohydrates (saccharides) to proteins and lipids. The glycosylationprocess is a co-translational and post-translational modification thattakes place during the synthesis of membrane and secreted proteins. Themajority of proteins synthesized in the rough endoplasmic reticulum (ER)undergo glycosylation (Brooks et al., Expert Rev Proteomics 3:345-59,2006). Glycosylation is an enzyme-directed, site-specific process,having two specific types of attachment, N-linked glycosylation andO-linked glycosylation. N-linked carbohydrates are attached viaN-acetylglucosamine linked to the amino acid asparagine at an amino acidconsensus sequence “Asn-X-Ser/Thr.” The surrounding amino acids oftendictate what type of, if any, glycosylation will take place. Forexample, if the middle amino acid in the consensus sequence is proline(Pro), no N-linked glycosylation takes place. Most O-linked carbohydratecovalent attachments to proteins involve a linkage between themonosaccharide N-acetylgalactosamine and the amino acids serine orthreonine (Werner et al., Acta Pediatrica 96:17-22, 2007). There is noconsensus sequence for O-linked glycosylation.

Glycosylation on protein may result in either addition of simple sugarresidues such as mannose and glucose, or addition of more complex sugarresidues such as sialic acid and fucose (Brooks et al., Expert RevProteomics 3:345-59, 2006), and branched chain sugars. Proteinglycosylation serves several functions in vivo, including stabilizationof the protein in the cytoplasm, increasing protein half-life, as wellas regulating the activity of the protein or enzyme having the glycosylresidues (Werner et al., Acta Pediatrica 96:17-22, 2007). Thus, it isimportant to ensure that proteins express the correct glycosylation orthe protein activity may be compromised or absent. The type ofglycosylation on a protein often depends on the cell type in which theprotein is synthesized, as well as the species of cell synthesizing theprotein (Werner et al., supra; Brooks et al., supra). For example,bacteria and yeast do not synthesize complex glycans which are typicallyfound on higher eukaryotic proteins (Brooks et al., supra). Even withinmammalian species (e.g., human and hamster), and from tumor cells tonormal, non-malignant cells, glycosylation patterns can be different(Werner et al., supra). Thus, the type of cell system in which theprotein is produced has a significant influence on the resultingglycosylated product (Werner et a)., supra).

Recombinantly produced proteins have provided a significant improvementto the study of proteins in both clinical and research settings. Thelarge scale production of recombinant proteins has enabled the study ofprotein activity in vitro, and recombinant proteins have recently beenused as therapeutic agents in the clinical setting. For example,recombinant interleukin-2 has been administered to cancer patients toboost the immune system after chemotherapy, and recombinant growthfactors, such as human growth hormone, erythropoietin and granulocytecolony stimulating factor, and blood factors, such as Factor VIII andFactor VII, are used in the treatment of various disorders.

Although recombinant proteins provide an advantage as therapeuticproteins, they also exhibit certain drawbacks. It can be difficult toproduce sufficient amounts of recombinant protein for therapeutic use inhuman cells in a cost efficient manner, and recombinant protein made insuch cells as Escherichia coli and other bacteria do not necessarilyfold properly, are not glycosylated, and/or must be manipulated onceisolated to manufacture proteins in a form active in the human body.Additionally, glycosylation of proteins in human cells is often morecomplex than that seen in commonly used protein expression systems, suchas bacteria, insects and even higher mammals. For example, insect cellssuch as Spodoptera rarely generate proteins having higher order sugarstructure of the types produced in mammals (Altmann et al.,Glycoconjugate J 16:109-123, 1999). Further, although most mammalsexpress higher order sugars comprising such structures as fucose andsialic acid residues, these sugar moieties may not be chemicallyattached in the same manner as the sugars in proteins produced in humancells (Jenkins et al., Nature Biotechnology 14:975-981, 1996; U.S. Pat.No. 5,047,335).

Administration of therapeutic proteins is often used in order to correcta deficiency or functional defect in the endogenously expressed protein.Recombinant insulin and insulin analogs (Vajo et al., Pharmacol Rev.52:1-9, 2000) are administered to diabetic patients to make up for thelack of naturally produced insulin Recombinant Factor VIII and sequenceanalogs of Factor VIII are administered to patients suffering fromhemophilia A to correct a deficiency in Factor VIII levels resulting inaberrant blood clotting (Gruppo et al., Haemophilia. 9:251-60, 2003). Inrecombinant therapies of these types, it is useful to determine thelevels of recombinant protein in serum or other sample in order todetermine the half-life of the drug and other pharmacokinetics, such asabsorption, in the patient. However, it can be difficult to determinethe difference between the endogenous protein and the recombinantprotein, since they are essentially the same protein.

Thus, there remains a need in the art to develop methods todifferentiate the amount of naturally-derived protein from the exogenousprotein in a sample and to detect the levels of endogenous and exogenousrecombinant protein administered to a patient in order that treatmentregimens may be optimized.

SUMMARY OF THE INVENTION

The present invention relates in general to methods for differentiatingthe presence of plasma-derived protein in a sample from a recombinantlyproduced protein in the sample, when the plasma-derived protein and therecombinant protein are essentially the same protein, by exploiting thedifference in glycosylation patterns between plasma proteins andrecombinant proteins. The invention also provides a method to quantitatethe levels of plasma-derived protein in a sample using the expression ofa particular carbohydrate moiety.

In one aspect, the invention provides a method to quantitate the amountof plasma-derived protein (pdP) and recombinant protein (rP) in asample, wherein the plasma-derived protein and recombinant protein arethe same protein with different glycosylation patterns, said differentglycosylation patterns giving rise to different degrees of lectinbinding for the plasma-derived protein compared to the recombinantprotein, wherein total protein (tP) in said sample is pre-determined andequal to the combined amounts of plasma-derived protein and recombinantprotein (pdP+rP), said method comprising the steps of: (a) calculating adifference between lectin binding for said sample and expected lectinbinding for a hypothetical sample of equal volume having an amount ofprotein equal to tP, wherein expected lectin binding is determined froma standard curve of lectin binding versus increasing amounts ofrecombinant protein, and, (b) plotting the difference from (a) on acalibration curve to determine the amount of recombinant protein (rP) insaid sample, wherein the calibration curve is a plot of the differencebetween expected lectin binding, calculated as in (a), and observedlectin binding for mixtures containing known amounts of pdP and rP, as afunction of increasing amounts of recombinant protein (_(rP)) in saidmixtures, said mixtures each having a constant amount of pdP.

In one embodiment, the calculating step comprises contacting the samplewith a lectin composition, wherein the lectin is labeled with adetectable label. The calculating step further comprises detecting thelabeled lectin composition using methods described herein in thedetailed description.

In a further embodiment, the method provides that the amount of totalprotein is pre-determined by measuring the amount of recombinant proteinand plasma-derived protein in a sample. The amount of total protein ismeasured using methods well-known in the art, such as, in one aspect, anenzyme linked immunosorbant assay (ELISA). In a related embodiment, theexpected lectin binding of a sample is determined by assuming that thetotal amount of protein in the sample is all plasma-derived protein andextrapolating the amount of lectin binding expected based on that amountof plasma-derived protein.

In an additional embodiment, the method provides that the calibrationcurve is prepared before quantitating the amount of plasma-derived andrecombinant protein in a sample. It is contemplated that the calibrationcurve is plotted as the difference between i) expected lectin binding ofa sample containing a known total amount of recombinant andplasma-derived protein and ii) the lectin binding observed for thosemixtures containing known amounts of pdP and rP, plotted as a functionof increasing amounts of rP in said mixtures, said mixtures each havinga constant amount of pdP.

In a related embodiment, the lectin is any lectin as described hereinwhich demonstrates specific binding to a sugar moiety found on a humanplasma-derived protein and not on the recombinant protein. In a specificembodiment, the lectin is Sambucus Nigra agglutinin (SNA).

It is further contemplated that the lectin is labeled with a detectablelabel. In one embodiment, the detectable label is selected from thegroup consisting of a fluorophore, a radioactive label, anelectron-dense reagent, an enzyme, biotin, digoxigenin, a hapten, or achemiluminescent agent. In a related embodiment, the label is biotin.

It is further contemplated that the sample is derived from a biologicalsample of a subject. In one embodiment, the sample is a blood sample. Ina related embodiment the sample is plasma. In a still furtherembodiment, the sample is serum.

The invention also provides that the plasma-derived protein and therecombinant protein are essentially the same protein, i.e., havegenerally the same amino acid structure and function. In one embodiment,the protein is a therapeutic protein, where in various aspects, theprotein is selected from the group consisting of a cytokine, a growthfactor, a blood clotting factor, an enzyme, a chemokine, a solublecell-surface receptor, a cell adhesion molecule, an antibody, a hormone,a cytoskeletal protein, a matrix protein, a chaperone protein, astructural protein, a metabolic protein, and any other therapeuticprotein known to those of skill in the art. In a further embodiment, theprotein is a blood clotting factor. In yet a further embodiment, theblood clotting factor is selected from the group consisting of vonWillebrand factor (vWF), Factor VIII (FVIII), Factor VII, and Factor IX(FIX).

In another aspect of the invention, the recombinant protein is producedin a host cell that lacks one or more glycosyltransferases such that therecombinant protein exhibits a different glycosylation pattern comparedto the glycosylation pattern of the plasma-derived protein. In variousembodiments, the host cell is a bacterial cell, a yeast cell, an insectcell, a plant cell, or a mammalian cell. In a related embodiment themammalian cell is a Chinese hamster ovary (CHO) cell.

The method of the invention provides for detection of a difference inglycosylation patterns between recombinantly produced protein andnaturally-occurring, plasma-derived protein. In one embodiment, theplasma-derived protein comprises a carbohydrate moiety that is not foundon the recombinant protein, wherein the carbohydrate moiety is selectedfrom those carbohydrate moieties known in the art and set out herein inthe detailed description. In a related embodiment, the plasma-derivedprotein comprises α2,6-neuraminic acid and the recombinant protein lacksα2,6-neuraminic acid.

In a further aspect of the invention, the method optionally comprisescontacting the sample with a binding agent specific for the proteinprior to contacting sample with the lectin composition. In oneembodiment, the binding agent is a ligand, soluble receptor, anantibody, a monoclonal antibody, a co-factor, or other protein thatbinds the plasma-derived protein or recombinant protein withspecificity.

In a related aspect, the method provides that the binding agent or theplasma-derived protein is bound on a solid support. In variousembodiments, the solid support is selected from the group consisting ofa filter, a membrane, including a polyvinyl choloride (PVC) membrane, apolyvinylidene fluoride (PDVF) membrane, a polyamide membrane, a plate,including a PVC plate, a polystyrene plate, and any other plate whichbinds protein, a microcarrier, a macro solid phase bead, a magnetic beadand a polysiloxane/polyvinyl alcohol bead.

In a further embodiment, the protein binding agent or plasma derivedprotein is in solution.

The method of the invention optionally comprises use of a blocking agentto prevent non-specific binding of the lectin protein to the sample. Themethod contemplates that the sample is contacted with the blocking agentafter contacting of sample with the binding agent. In one embodiment,the blocking agent is selected from the group consisting of serumalbumin, gelatin, glycosidase solutions, carbohydrate-modifying agents,such as acetylating agents or methylating agents, and a carbohydrateoxidizing solution. In one embodiment, the carbohydrate oxidizingsolution is a periodate solution.

In another aspect of the invention, it is contemplated that a methodrecited herein utilizes a recombinant protein that is a fragment,variant or analog of the plasma-derived protein.

The invention also provides a method to differentiate plasma-derivedprotein from recombinant protein in a sample comprising, contacting thesample with a composition comprising a lectin specific for acarbohydrate moiety on the plasma-derived protein; detecting binding ofthe lectin to the plasma-derived protein; and comparing the amount ofbinding of protein-bound lectin in the sample to a lectin:proteinbinding curve to determine the amount of plasma-derived protein in thesample.

In one embodiment, the lectin is Sambucus nigra agglutinin (SNA)protein. In a related embodiment, the lectin is labeled with adetectable label as described herein.

In yet another aspect, the invention provides a kit for quantitatinglevels of plasma derived protein and recombinant protein in a sample,wherein the plasma-derived protein and the recombinant protein encodethe same protein, the kit comprising, a binding agent; a compositioncomprising a lectin specific for a carbohydrate on the plasma-derivedprotein and a detectable label, and a protein standard. In oneembodiment, the kit optionally comprises a blocking agent.

Other features and advantages of the invention will become apparent fromthe following detailed description. It should be understood, however,that the detailed description and the specific examples, whileindicating specific embodiments of the invention, are given by way ofillustration only, because various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plot of a four-point calibration curve correlating thedifference in expected and observed SNA binding in a sample with theamount of recombinant protein.

FIG. 2 is a plot of an eight-point calibration curve correlating thedifference in expected and observed SNA binding in a sample with theamount of recombinant protein

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates, in general, to methods fordifferentiating plasma-derived protein from recombinantly producedprotein in a sample based on the difference in protein glycosylationbetween the two types of proteins. The invention further contemplatesmethods to quantitate the amount of plasma-derived protein in a samplecomprising both recombinant protein and plasma-derived protein, whereinthe plasma-derived protein and the recombinant protein comprise thesame, or essentially the same, amino acid sequence.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The following referencesprovide one of skill with a general definition of many of the terms usedin this invention: Singleton, et al., DICTIONARY OF MICROBIOLOGY ANDMOLECULAR BIOLOGY (2d ed. 1994); THE CAMBRIDGE DICTIONARY OF SCIENCE ANDTECHNOLOGY (Walker ed., 1988); THE GLOSSARY OF GENETICS, 5TH ED., R.Rieger, et al. (eds.), Springer Verlag (1991); and Hale and Marham, THEHARPER COLLINS DICTIONARY OF BIOLOGY (1991).

Each publication, patent application, patent, and other reference citedherein is incorporated by reference in its entirety to the extent thatit is not inconsistent with the present disclosure.

It is noted here that as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referenceunless the context clearly dictates otherwise.

As used herein, the following terms have the meanings ascribed to themunless specified otherwise.

As used herein a “polypeptide” refers to a polymer composed of aminoacid residues linked via peptide bonds. Synthetic polypeptides can besynthesized, for example, using an automated polypeptide synthesizer.The term “protein” typically refers to large polypeptides. The term⁻peptide” typically refers to short polypeptides. As used herein,polypeptide protein and peptide are used interchangeably.

As used herein a “fragment” of a polypeptide refers to any portion ofthe polypeptide smaller than the full-length polypeptide or proteinexpression product. Fragments are typically deletion analogs of thefull-length polypeptide wherein one or more amino acid residues havebeen removed from the amino terminus and/or the carboxy terminus of thefull-length polypeptide. Accordingly, “fragments” are a subset ofdeletion analogs described below.

As used herein an “analog” refers to a polypeptide substantially similarin structure and having the same biological activity, albeit in certaininstances to a differing degree, to a naturally-occurring molecule.Analogs differ in the composition of their amino acid sequences comparedto the naturally-occurring polypeptide from which the analog is derived,based on one or more mutations involving (i) deletion of one or moreamino acid residues at one or more termini of the polypeptide and/or oneor more internal regions of the naturally-occurring polypeptidesequence, (ii) insertion or addition of one or more amino acids at oneor more termini (typically an “addition” analog) of the polypeptideand/or one or more internal regions (typically an “insertion” analog) ofthe naturally-occurring polypeptide sequence or (iii) substitution ofone or more amino acids for other amino acids in the naturally-occurringpolypeptide sequence. Substitutions can be conservative ornon-conservative based on the physico-chemical or functional relatednessof the amino acid that is being replaced and the amino acid replacingit.

As used herein a “variant” refers to a protein or analog thereof that ismodified to comprise additional chemical moieties not normally a part ofthe molecule. Such moieties may improve the molecule's solubility,absorption, biological half-life, etc. The moieties may alternativelydecrease the toxicity of the molecule and eliminate or attenuate anyundesirable side effect of the molecule, etc. Moieties capable ofmediating such effects are disclosed in Remington's PharmaceuticalSciences (1980). Procedure for coupling such moieties to a molecule arewell known in the art. For example, the variant may be a blood clottingfactor having a chemical modification which confers a longer half-lifein vivo to the protein. In certain aspects, variants are polypeptidesthat are modified by glycosylation, pegylation, or polysialylation.

As used herein, “naturally-occurring,” as applied to a protein orpolypeptide, refers to the fact that the protein can be found in nature.For example, a polypeptide or polynucleotide sequence that is present inan organism (including viruses) that can be isolated from a source innature and which has not been intentionally modified by man in thelaboratory is naturally-occurring. The terms “naturally-occurring” and“wild-type” are used interchangeably throughout.

As used herein, “plasma-derived,” as applied to a protein orpolypeptide, refers to a naturally-occurring polypeptide or fragmentthereof that is found in blood plasma or serum of a subject. Aplasma-derived protein may also be a naturally-occurring protein and awild-type protein.

As used herein “are the same protein or essentially the same protein”refers to a naturally-occurring protein (e.g., a plasma-derived protein)which may also be expressed recombinantly by genetic engineering,resulting in a recombinant protein having the same or essentially thesame amino acid sequence as the naturally derived protein. A recombinantprotein which is the same protein as a naturally-produced,plasma-derived protein includes fragments, analogs and variants of thefull-length recombinant protein.

As used herein, “expected lectin binding” refers to the hypotheticallectin binding of a sample as determined by assuming that the totalamount of protein in the sample is all in plasma-derived protein, andextrapolating the amount of lectin binding expected based on thehypothetical amount of plasma-derived protein when compared to alectin:protein standard binding curve.

As used herein a “detectable moiety,” “detectable label” or “label”refers to a composition detectable by spectroscopic, photochemical,biochemical, immunochemical, or chemical means. For example, usefullabels include ³²P, ³⁵S, fluorescent dyes, electron-dense reagents,enzymes (e.g., as commonly used in an ELISA), biotin-streptavidin,dioxigenin, haptens and proteins for which anti-sera or monoclonalantibodies are available, or nucleic acid molecules with a sequencecomplementary to a target. The detectable moiety often generates ameasurable signal, such as a radioactive, chromogenic, or fluorescentsignal, that can be used to quantitate the amount of bound detectablemoiety in a sample.

As used herein the terms “express,” “expressing” and “expression” referto allowing or causing the information in a gene or DNA sequence tobecome manifest, for example by producing a protein by activating thecellular functions involved in transcription and translation of acorresponding gene or DNA sequence. A DNA sequence is expressed in or bya host cell to form an “expression product” such as a protein. Theexpression product itself, e.g. the resulting protein, may also be saidto be “expressed” or “produced” by the host cell.

Fragments, Variants and Analogs

Methods of the invention are useful to rapidly detect recombinantproteins in a sample, as well as fragments, variants or analogs of therecombinant protein, and further may be useful to detectnaturally-occurring protein which may exist as fragments or allelicvariants in vivo wherein glycosylation differences can be detected.

Methods for preparing polypeptide fragments, variants or analogs arewell-known in the art. Fragments of a polypeptide are prepared usingmethods well known in the art, including enzymatic cleavage (e.g.,trypsin, chymotrypsin) and also using recombinant means to generate apolypeptide fragment having a specific amino acid sequence. Fragmentsmay be generated to comprise a ligand binding domain, a receptor bindingdomain, a dimerization or multimerization domain, or any otheridentifiable domain known in the art.

Methods of making polypeptide analogs are also well-known. Analogs maybe substantially homologous or substantially identical to thenaturally-occurring polypeptide from which the analog is derived, andanalogs contemplated by the invention are those which retain at leastsome of the biological activity of the naturally-occurring polypeptide.

Substitution analogs typically exchange one amino acid of the wild-typefor another at one or more sites within the protein, and may be designedto modulate one or more properties of the polypeptide, such as stabilityagainst proteolytic cleavage, without the loss of other functions orproperties. Substitutions of this kind are generally conservative. By“conservative amino acid substitution” is meant substitution of an aminoacid with an amino acid having a side chain of a similar chemicalcharacter. Similar amino acids for making conservative substitutionsinclude those having an acidic side chain (glutamic acid, asparticacid); a basic side chain (arginine, lysine, histidine); a polar amideside chain (glutamine, asparagine); a hydrophobic, aliphatic side chain(leucine, isoleucine, valine, alanine, glycine); an aromatic side chain(phenylalanine, tryptophan, tyrosine); a small side chain (glycine,alanine, serine, threonine, methionine); or an aliphatic hydroxyl sidechain (serine, threonine).

Polynucleotide analogs and fragments may be readily generated by aworker of skill to encode biologically active fragments, variants, ormutants of the naturally occurring molecule that possess the same orsimilar biological activity to the naturally occurring molecule.Routinely practiced methods include PCR techniques, enzymatic digestionof DNA encoding the protein molecule and ligation to heterologouspolynucleotide sequences, and the like. For example, point mutagenesis,using PCR and other techniques well-known in the art, may be employed toidentify with particularity which amino acid residues are important inparticular activities associated with protein activity. Thus, one ofskill in the art will be able to generate single base changes in the DNAstrand to result in an altered codon and a missense mutation.

It is further contemplated that the protein or polypeptide may bemodified to make an analog which is a fusion protein comprising a secondagent which is a polypeptide. In one embodiment, the second agent whichis a polypeptide is an enzyme, a growth factor, a cytokine, a chemokine,a cell-surface receptor, the extracellular domain of a cell surfacereceptor, a cell adhesion molecule, or fragment or active domain of aprotein described above or of any other type of protein known in theart. In a related embodiment, the second agent is a blood clottingfactor such as Factor VIII, Factor VII, Factor IX and von Willebrandfactor. The fusion protein contemplated is made by chemical orrecombinant techniques well-known in the art.

Protein variants contemplated include polypeptides chemically modifiedby such techniques as ubiquitination, glycosylation, conjugation totherapeutic or diagnostic agents, labeling (e.g., with radionuclides orvarious enzymes), covalent polymer attachment such as pegylation(derivatization with polyethylene glycol), introduction ofnon-hydrolyzable bonds, and insertion or substitution by chemicalsynthesis of amino acids such as ornithine, which do not normally occurin human proteins. Variants retain the binding properties ofnon-modified molecules of the invention.

Preparing pegylated variants of a polypeptide, fragment or analogs willgenerally comprise the steps of (a) reacting the polypeptide withpolyethylene glycol (such as a reactive ester or aldehyde derivative ofPEG) under conditions whereby the binding construct polypeptide becomesattached to one or more PEG groups, and (b) obtaining the reactionproduct(s). In general, the optimal reaction conditions for theacylation reactions will be determined based on known parameters and thedesired result. For example, the larger the ratio of PEG:protein, thegreater the percentage of poly-pegylated product. In some embodiments,the binding construct will have a single PEG moiety at the N-terminus.Polyethylene glycol (PEG) may be attached to the protein to provide alonger half-life in vivo. The PEG group may be of any convenientmolecular weight and may be linear or branched. The average molecularweight of the PEG will range from about 2 kiloDalton (“kDa”) to about100 kDa, more from about 5 kDa to about 50 kDa, most from about 5 kDa toabout 10 kDa. The PEG groups will generally be attached to the bloodclotting factor via acylation or reductive alkylation through a naturalor engineered reactive group on the PEG moiety (e.g., an aldehyde,amino, thiol, or ester group) to a reactive group on the blood clottingfactor (e.g., an aldehyde, amino, or ester group).

Additional polypeptide variants useful in the methods of the presentinvention include polypeptide comprising polysialylate (PSA) moieties.Methods for preparing polysialylated polypeptide are described in UnitedStates Patent Publication 20060160948 and Saenko et al., Haemophilia12:42-51, 2006.

Glycosylation

Glycosylation in human proteins is composed of combinations of simpleand complex sugars. Monosaccharides such as mannose, glucose, fucose,galactose, N-acetylgalactosamine, N-acetylglucosamine, and sialicacid/neuraminic acid are combined into linear or branched chains ofabout two to up to twelve or more monosaccharides (Brooks et al., ExpertRev Proteomics 3:345-59, 2006). Each monosaccharide may be linked toanother sugar moiety by either alpha or beta linkages at any of thecarbons on the next structure, e.g, α1-3 linkage between first carbon onthe first sugar and the third carbon on the next sugar. Addition ofsugar moieties is carried out by specific glycosyltransferases andsugars are removed by sugar-specific glycosidase proteins.

In N-glycosylation, the base sugar moiety comprising nine mannoseresidues, two N-acetylgalactosamine residues and three glucose residues(GalNac₂Man₉Glc₁) is attached to an asparagine residue in the protein.Once attached to the protein the oligosaccharide is trimmed to removethe terminal three glucose residues and a mannose residue. The proteinis then transported to the Golgi apparatus where further posttranslational modification takes place, e.g., an additional threemannose moieties are removed leaving a core sugar of five mannose andtwo N-acetylglucosamine (Man₅GlcNac₂). This moiety may be trimmedfurther or additional residues added. Several higher orderoligosaccharides are based off a core structure having three mannose andtwo N-acetylglucosamine sugars. High mannose contains between five andnine mannose residues linked to the core structure. Complexoligosaccharides comprise N-acetylglucosamine residues substituted forα1,3- and α1,6 linked mannose residues. Hybrid oligosaccharides compriseN-acetylglucosamine residues in place of α1,3-linked mannose residues.Hybrid and complex N-linked oligosaccharides are not synthesized bysimple organisms such as yeast and bacteria.

O-glycosylation is a post-translational event that takes place in theGolgi apparatus and begins with linkage of a single monosaccharide,typically N-acetyl galactosamine, but may be a mannose or fucose, to anOH group of a serine or threonine residue. Further chain extension iscarried out in a stepwise manner, but there is no core structurerequired for addition as in N-linked glycosylation (Brooks et al.,supra).

Bacteria attach sugar residues to proteins in a wholly different mannerthan the process in mammalian cells due to a lack of Golgi apparatusother organelles. Most bacterial glycoproteins lack sialic acid moietiesin N-glycosylated proteins, or if sialic acid is present, the residuesoften occur in polysialic acid chains similar to those produced in humanneural cell proteins (Brooks et al, supra), but not in typicalglycoproteins. The enzyme α2,3 sialyltransferase, responsible forattaching α2,3 sialic acid, has been isolated in N. gonorrhoeae. Geneticengineering has been attempted to introduce either bacterial or humanglycosyltransferases into bacterial cells in an attempt to produceproteins having glycosylation more similar to that of human proteins. InO-linked glycosylation, bacterial O-glycans are highly methylated andcontain the sugar rhamnose which is not found in humans. Also, the firstmonosaccharide added need not be GalNac.

Yeast (e.g., Pichia pastoris, S. Cerevisiae) carry out the first stagesof N-glycosylation similar to human cells, generating the nine mannose,three glucose, two N-acetylglucosamine core oligosaccharide andattaching it to the protein. The nine-mannose core is then trimmed toonly an eight mannose, two N-acetylglucosamine core. This eight-mannosestructure is not trimmed as in human cells, but may be furthermannosylated to contain up to 100 mannose residues (Brooks et al.,supra). Engineered Pichia pastoris cells have been developed whichexpress glycosyltransferase enzymes which attach sugar residues in amanner that more closely resembles attachment in human proteins (Brookset al,. supra, Gerngross et al., Nat Biotechnol. 22:1409-14, 2004; Wildtet al., Nat Rev Microbiol 3:119-128, 2005). However, successfulintroduction of sialyltransferase enzymes has not been achieved, leavingmost proteins produced in yeast cells lacking sialyl residues (Brooks etal., supra). Yeast O-glycosylation begins with a mannose residue linkedto a serine or threonine residue, and may be extended up to five mannoseresidues in either a branched or linear configuration. Mannose-linkedO-glycosylation does not occur in humans.

Plant cell protein glycosylation differs widely from that in humans.N-glycosylation in plant cells begins like that in human cells, in whicha core oligosaccharide GalNac₂Man₉Glc₃ is formed. This core structure isthen trimmed to a moiety having five to nine mannose residues and twoN-acetylglucosamine residues (Man₅₋₉GlcNac₂) that may be furtherextended using sugars such as fucose and xylose (a non-human sugar) inlinkage arrangements which are not expressed in human cells and can beimmunogenic to humans. Plant glycoproteins are generally thought to beunsialylated, but may be induced to add sialyl groups in culture(Saint-Jore-Dupas et al., Trends in Biotechnol 25: 317-23, 2007).Recently attempts have been made to produce engineered plant cells whichexpress the necessary machinery to produce sialylated proteins (Paccaletet a)., Plant Biotechnol. J 5:16-25, 207). In order for plants toexpress sialic acid, the entire group of human genes responsible forthis glycosylation, including sialic acid synthetases,glycosyltransferases and transporters, must be transduced into plantcells, making expression of sialylated plant proteins difficult. PlantO-linked glycosylation may be attached at serine, threonine orhydroxyproline residues. O-linked glycans in plant include the sugarsrhamnose, arabinose and glucuronic acid which are not found in humans,as well as more mammalian-type structures, such as GalNac.

Glycosylation in insect cells proceeds similarly to that in plant cells.The N-glycan precursor core is synthesized and added to proteins andtrimmed to the tri-mannose core structure. However, further modificationis generally restricted to addition of mannose or fucose residues(Brooks et al. supra, Altmann et al., Glycoconjugate J 16:109-123,1999). Insect cells characteristically produce unsialylated proteins,but may be induced to produce sialyl acid in certain culture conditions,and during certain stages of development (Brooks et al., supra; Tomiyaet al., Glycoconj J. 21:343-360, 2004). Insect cells have beenengineered to express human sialyltransferase genes with moderatesuccess at generating sialylated proteins (Aumiller et al., Glycobiology13:497-507, 2003). However, insect cells secrete a sialidase enzymewhich can cleave of any sialic acid moieties added to the proteins.O-linked glycosylation is similar to that in humans.

Glycosylation in non-human mammalian cells, such as baby hamster kidney(BHK) and Chinese hamster ovary (CHO) cells, which are the mostprevalent cell lines to produce therapeutic proteins on a large scale,often produce proteins with glycosylation moieties similar to humanprotein, but not exactly the same. For example CHO cells express adifferent sialic-acid-like sugar moiety and therefore do not producesialic acid as produced in human cells (Brooks et al., Ext RevProteomics 3:345-59, 2006); Chenu et al., Biochem Biophys Acta1622:133-44, 2003). Further, CHO cells assemble the sialic acid likesugar in an α2,3 configuration which is not expressed in human cells.Modified CHO cells engineered to express the human α2,6sialyltransferase successfully produce proteins expressing both ahuman-type α2,6 sialic acid and the hamster-derived α2,3 sialic acid(Bragonzi et al., Biochem Biophys Acta 1474:273-82, 2000). Little isknown about O-glycosylation in insects. Insects are believed toO-glycosylate threonine residues, and can include such mammalian-likesugars such as GalNac, and the disaccharide GalNac plus galactose.

Lectin Proteins

Sugar moieties are specifically bound by lectin proteins, which arecarbohydrate-binding proteins or glycoproteins which are highly specificfor particular sugar moieties. Lectin proteins were first isolated fromplant species, e.g., the lectin Sambucus nigra agglutinin (SNA) isisolated from the elderberry tree, and specifically binds α2,6 sialicacid moieties (Brinkman-Van der Linden et al., Analytical Biochemistry303:98-104, 2002). Lectin proteins are also now known to be found inalmost all species.

The binding of lectins to their corresponding carbohydrates can beeither Ca²⁺-dependent or Ca²⁺-independent. See U.S. Pat. No. 5,225,542.The specificity of the lectin recognition of carbohydrates is highlyspecific and thus comparable to the antigen-specificity of antibodies orthe substrate-specificity of enzymes. For example, severalCa²⁺-independent lectins have been isolated from bovine pancreas andwhich can specifically the β-galactosides lactose and asialofetuin andthe α-galactoside melibiose, and to Ca²⁺-dependent fuscose bindinglectins have also been identified.

The lectin Maackia amurensis agglutinin (MAA, MAL) binds α2,3 sialicacid, Sambucus nigra agglutinin (SNA) binds α2,6 sialic acid, Aleuriaaurantia lectin (AAL) (Kobata and Yamashita, 1993) and Lens culinaris(LcH) (Yamashita et al., 1993) bind fucose residues. Several plantlectins are specific for N-acetyl-β-D-galactosamine, which is a bloodgroup specific carbohydrate, and are used in blood group typing. C-typeanimal lectins bind N-Acetylgalactosamine. Limulin and Limax flavusagglutinin (LFA) strongly interact with O-chain glycoproteins. (Fischeret al., Glycoconjugate J. 12:707-13, 2004). In addition, lectin analogshave been developed to mimic the action of natural analogs, but withgreater specificity (Ferrand et al., Science 318:619-622, 2007).

The tables* below detail known lectins and their binding specificityuseful in the methods of the invention.

Lectin name Organism Binding Specificity Mannose binding lectins Con AConcanavalin A Canavalia branched α-mannosidic structures; ensiformishigh-mannose type, hybrid type and biantennary complex type N- GlycansLCH Lentil lectin Lens Fucosylated core region of bi- and culinaristriantennary complex type N-Glycans GNA Snowdrop lectin Galanthus α 1-3and α 1-6 linked high mannose nivalis structuresGalactose/N-acetylgalactosamine binding lectins RCA Ricinus communisRicinus Galβ1-4GlcNAcβ1-R Agglutinin, RCA₁₂₀ communis PNA PeanutAgglutinin Arachis Galβ1-3GalNAcα1-Ser/Thr (T-Antigen) hypogaea AILJacalin Artocarpus (Sia)Galβ1-3GalNAcα1-Ser/Thr integrifolia (T-Antigen)VVL Hairy vetch lectin Vicia villosa GalNAcα-Ser/Thr (Tn-Antigen) Sialicacid/N-acetylglucosamine binding lectins WGA Wheat Germ agglutininTriticum vulgaris GlcNAcβ1-4GlcNAcβ1-4GlcNAc, Neu5Ac (sialic acid) SNAElderberry lectin Sambucus nigra Neu5Acα2-6Gal(NAc)-R MAL Maackiaamurensis lectin Maackia Neu5Ac/Gcα2-3Galβ1-4GlcNAcβ1-R amurensis Fucosebinding lectins UEA Ulex europaeus agglutinin Ulex europaeusFucα1-2Gal-R AAL Aleuria aurantia lectin Aleuria aurantiaFucα1-2Galβ1-4(Fucα1-3/4)Galβ1- 4GlcNAc; R₂-GlcNAcβ1-4(Fucα1-6)GlcNAc-R₁Lectin name Abbreviation Binding Specificity Agaricus ABA Fetuin;Galβ1-3GalNAc bisporus Amaranthus ACL Galβ 1-3GalNAc, Neu5Acα2-3Galβ1-3GalNAc; T-Antigen caudatus Griffonia GSL I α-N-acetylgalactosamine,α-galactose simplicifolia lectin I Griffonia GSL II terminal-α,β-GlcNAc;glycogen simplicifolia lectin II Griffonia GSL I B4 α-D-galactosylresidues simplicifolia I B4 Bauhinia BPL Galβ1-3GalNAc purpurea albaCodium fragile CFL GalNAc Datura DSL (GlcNAcβ1-4)₃GlcNAc =(Glcβ1-4)₂GlcNAc > Glcβ1-4GlcNAc >> stramonium GlcNAc Dolichos biflorusDBA terminal FP > GalNAcα1-3GalNAc > GalNAcα1-3Gal; blood group A₁(Forssman pentasaccharide: GalNAcα1-3GalNAcα1- 3Galβ1-4Galβ1-4GlcNAc)Erythrina ECor A GalNAc/N-acetyllactosamin/Lactose/D-Gal coralldendronEuonymos EEA Galα1-3(L-Fucα1-2)Galβ1,3/4-β-GlcNAc; Galα1-3Gal; bloodeuropaeus group H structures Glycine max SBA terminal α,βGalNAc > α,βGalHelix aspersa HAA terminal αGalNAc residues Helix pomatia HPAGalNAcα1-3GalNAc > α-GalNAc > α-GlcNAc >> α-Gal Hippeastrum HHL(α1,3)/(α1,6) mannose; polymannose structures; yeast hybridgalactomannans Lotus LTL α-L-fucose tetragonolobus Lycopersicon LEL(GlcNAcβ 1-4)₃ GlcNAc > (GlcNAcβ1-4)₂ GlcNAc > GlcNAcβ1- esculentum4GlcNAc Maclura MPA terminal Galβ1-3GalNAc > GalNAcα 1-6Gal pomiferaNarcissus NPA terminal and internal α-D-mannosylresidues onglycoconjugates, pseudonarcissus preferably oligomannoses containingα1-6 linkages Phaseolus PCA agglutination is not inhibited bymonosaccharides but is inhibited coccineus by fetuin Phaseolus PHA-LGlcNAcβ1,2Man, triantennary complex oligosaccharides vulgaris LPhaseolus PHA-E Galβ1,4GlcNAcβ1,2Manα1,6 vulgaris E Phytolacca PWMN-acetyl-β-D-glucosamine oligomers americana Pisum sativum PSA, PEAbranched α-man, complex type with N-acetylchitobiose-linked core α-fucPsophocarpus PTL, WBA α-galactosamine tetragonolobus I Solanum STAN-acetyl-β-D-glucosamine oligomers tuberosum Sophora SJA Galβ1,3GalNAc >Galβ 1,3GlcNAc > αβ,GalNAc > αβ,Gal japonica terminal Wisteria WFA, WFLterminal N-acetylgalactosamine-α- or β-3 or 6-galactose floribunda*Tables adapted from Galab Technologies GmbH, Germany, citing Gabius,H.-J.; Gabius, S. (Eds.): Glycosciences - Status and Perspectives.Weinheim: Chapman & Hall, 1997; Goldstein, et al., Sharon, N.;Goldstein, I. J. (Eds.) The Lectins - Properties, Functions andApplications in Biology and Medicine. Orlando: Academic Press, 1986, S.33-243; Debray et al., Eur. J. Biochem., 117, 41-55, 1981.

The lectins described above may be used in the methods of the inventionto differentiate the glycosylation patterns of two different proteins,which may be dependent on the expression source of the protein. Forexample, the SNA protein as exemplified in the examples below is usefulto specifically bind proteins expressing α2,6 sialic acid residues whilethe MAA protein specifically binds α2,3 sialic acid residues.

Recombinant Proteins

Methods for making recombinant proteins are well-known in the art.Methods of producing cells, including mammalian cells, which express DNAor RNA encoding a recombinant protein are described in U.S. Pat. Nos.6,048,729, 5,994,129, and 6,063,630. The teachings of each of theseapplications are expressly incorporated herein by reference in theirentirety.

A nucleic acid construct used to express a polypeptide or fragment,variant or analog thereof can be one which is expressedextrachromosomally (episomally) in the transfected mammalian cell or onewhich integrates, either randomly or at a pre-selected targeted sitethrough homologous recombination, into the recipient cell's genome. Aconstruct which is expressed extrachromosomally comprises, in additionto polypeptide-encoding sequences, sequences sufficient for expressionof the protein in the cells and, optionally, for replication of theconstruct. It typically includes a promoter, a polypeptide-encoding DNAsequence and a polyadenylation site. The DNA encoding the protein ispositioned in the construct in such a manner that its expression isunder the control of the promoter. Optionally, the construct may containadditional components such as one or more of the following: a splicesite, an enhancer sequence, a selectable marker gene under the controlof an appropriate promoter, and an amplifiable marker gene under thecontrol of an appropriate promoter.

In those embodiments in which the DNA construct integrates into thecell's genome, it need include only the polypeptide-encoding nucleicacid sequences. Optionally, it can include a promoter and an enhancersequence, a polyadenylation site or sites, a splice site or sites,nucleic acid sequences which encode a selectable marker or markers,nucleic acid sequences which encode an amplifiable marker and/or DNAhomologous to genomic DNA in the recipient cell to target integration ofthe DNA to a selected site in the genome (targeting DNA or DNAsequences).

Host cells used to produce recombinant proteins are bacterial, yeast,insect, non-mammalian vertebrate, or mammalian cells; the mammaliancells include, but are not limited to, hamster, monkey, chimpanzee, dog,cat, bovine, porcine, mouse, rat, rabbit, sheep and human cells. Thehost cells can be immortalized cells (a cell line) or non-immortalized(primary or secondary) cells and can be any of a wide variety of celltypes, such as, but not limited to, fibroblasts, keratinocytes,epithelial cells (e.g., mammary epithelial cells, intestinal epithelialcells), ovary cells (e.g., Chinese hamster ovary or CHO cells),endothelial cells, glial cells, neural cells, formed elements of theblood (e.g., lymphocytes, bone marrow cells), muscle cells, hepatocytesand precursors of these somatic cell types.

Commonly used host cells include: Prokaryotic cells such as warnnegative or gram positive bacteria, i.e., any strain of E. coli,Bacillus, Streptomyces, Saccharomyces, Salmonella, and the like;eukaryotic cells such as CHO (Chinese hamster ovary) cells; baby hamsterkidney (BHK) cells; human kidney 293 cells; COS-7 cells; insect cellssuch as D. Mel-2, Sf4, Sf5, Sf9, and Sf21 and High 5; plant cells andvarious yeast cells such as Saccharomyces and Pichia.

Host cells containing the polypeptide-encoding DNA or RNA are culturedunder conditions appropriate for growth of the cells and expression ofthe DNA or RNA. Those cells which express the polypeptide can beidentified, using known methods, and the recombinant protein isolatedand purified, using known methods; either with or without amplificationof polypeptide production. Identification can be carried out, forexample, through screening genetically modified mammalian cellsdisplaying a phenotype indicative of the presence of DNA or RNA encodingthe protein, such as PCR screening, screening by Southern blot analysis,or screening for the expression of the protein. Selection of cellshaving incorporated protein-encoding DNA may be accomplished byincluding a selectable marker in the DNA construct and culturingtransfected or infected cells containing a selectable marker gene underconditions appropriate for survival of only those cells that express theselectable marker gene. Further amplification of the introduced DNAconstruct can be affected by culturing genetically modified cells underconditions appropriate for amplification (e.g., culturing geneticallymodified cells containing an amplifiable marker gene in the presence ofa concentration of a drug at which only cells containing multiple copiesof the amplifiable marker gene can survive).

Recombinant proteins which can be therapeutic proteins include, but arenot limited to, cytokines, growth factors, blood clotting factors,enzymes, chemokines, soluble cell-surface receptors, cell adhesionmolecules, antibodies, hormones, cytoskeletal proteins, matrix proteins,chaperone proteins, structural proteins, metabolic proteins, and othertherapeutic proteins known to those of skill in the art. Exemplaryrecombinant proteins which are/may be used as therapeutics include, butare not limited to, Factor VIII, Factor VII, Factor IX and vonWillebrand factor, erythropoietin, interferons, insulin, CTLA4-Ig,alpha-glucocerebrosidase, alpha-glucosidase, follicle stimulatinghormone, anti-CD20 antibody, anti-HER2 antibody, anti-CD52 antibody, TNFreceptor, and others known in the art. See, for example, Physicians DeskReference, 62^(nd) Edition, 2008, Thomson Healthcare, Montvale, N.J.

Methods of Detecting Protein in a Sample

Therapeutic proteins are often difficult to detect in serum samples dueto their similarity to the endogenously produced, naturally-occurringprotein. However, it is often beneficial to determine the amount of atherapeutic polypeptide, fragment, variant or analog thereof that hasbeen administered to assess whether the therapeutic protein exhibitsdesired characteristics such as greater solubility or stability,resistance to enzyme digestion, improved biological half-life, and otherfeatures known to those skilled in the art. The method also allows fordetection of authorized uses of therapeutic proteins which may beprotected by intellectual property rights.

The present invention provides a method to differentiate plasma-derivednaturally-occurring proteins from recombinant proteins in a sample,thereby allowing quantitation of each type of protein in a sample. Theability to identify the amount of recombinant protein in a sample overtime aids in determination of the optimal therapeutic based onhalf-life, absorption, stability, etc. The detection assay may be anenzyme linked immunosorbant assay (ELISA), a radioimmunoassay (RIA), ascintillation proximity assay (SPA), surface plasma resonance (SPR), orother binding assays known in the art.

The methods of detection set out herein utilize the difference inglycosylation patterns between plasma-derived proteins and that of manyrecombinantly produced proteins, as described above.

In order to detect plasma-derived protein in a sample, the sample iscontacted with a composition comprising a lectin protein describedherein that is specific for a carbohydrate moiety on the plasma-derivedprotein, and the amount of lectin-bound plasma-derived protein ismeasured. In one aspect, the contacting step is performed in a liquidenvironment such as an aqueous buffer, such as phosphate buffered saline(PBS), magnesium/calcium-free PBS, or other appropriate buffers as knownin the art. See, for example, Current Protocols in Protein Science,Coligan et al., Eds.,1998, John Wiley and Sons, Hoboken, N.J. It iscontemplated that contacting in the method of the invention is carriedout for a time period sufficient for binding to reach equilibrium andtypically for a time in the range of 15 minutes to overnight. Forexample, the sample is contacted with the either a binding agent or alectin protein, for 15 minutes, 30 minutes, 45 minutes, 1 hour, 2 hours,3 hours, 4 hours, 6 hours, 8 hours, 12 hours, 14 hours, 16 hours, 18hours, 20 hours, 24 hours, or a time appropriate for sufficient bindingfor the binding agent or the lectin to the plasma-derived protein.

The method optionally includes at least one or more washing steps,wherein the bound lectin:protein composition is washed prior tomeasuring protein binding to reduce background measurements caused byunbound polypeptides. Washing of the lectin after incubation of thepolypeptide composition and before detection of lectin:protein bindingis performed in appropriate buffer plus detergent. Suitable detergentsinclude, but are not limited to alkyldimethylamine oxides, alkylglucosides, alkyl maltosides, alkyl sulfates (such as sodium dodecylsulfate (SDS)), NP-40, alkyl thioglucosides, betaines, bile acids, CHAPseries, digitonin, glucamides, lecithins/lysolecithins, nonionicpolyoxyethylene-based detergents, including TRITON-X, polysorbates, suchas TWEEN® 20 and TWEEN® 80, BRIJ®, GENAPOL® and THESIT®, quaternaryammonium compounds, and the like. See also Current Protocols in ProteinScience, Appendix 1B, Suppl. 11, 1998, John Wiley and Sons, Hoboken,N.J. Suitable detergents can be determined using routine experimentation(see Neugebauer, J., A Guide to the Properties and Use of Detergents inBiology and Biochemistry, Calbiochem-Novabiochem Corp., La Jolla,Calif., 1988).

As discussed above, the lectin protein may be linked to a detectablemoiety or a detectable label. Detectable moiety or label refers to acomposition detectable by spectroscopic, photochemical, biochemical,immunochemical, or chemical means. The detectable moiety often generatesa measurable signal, such as a radioactive, chromogenic, or fluorescentsignal, that can be used to quantitate the amount of bound detectablemoiety in a sample. The detectable moiety can be incorporated in orattached to the protein either covalently, or through ionic, van derWaals or hydrogen bonds, e.g., incorporation of radioactive nucleotides,or biotinylated nucleotides that are recognized by streptavidin. Thedetectable moiety may be directly or indirectly detectable. Indirectdetection can involve the binding of a second directly or indirectlydetectable moiety to the detectable moiety. For example, the detectablemoiety can be the ligand of a binding partner, such as biotin, which isa binding partner for streptavidin. The binding partner may itself bedirectly detectable, for example, an antibody may be labeled with afluorescent molecule. Selection of a method quantitation of the signalis achieved by, e.g., scintillation counting, densitometry, or flowcytometry.

Examples of labels suitable for use in the assay methods of theinvention include, radioactive labels, fluorophores, electron-densereagents, enzymes (e.g., as commonly used in an ELISA), biotin,digoxigenin, or haptens as well as proteins which can be madedetectable, e.g., by incorporating a radiolabel into the hapten orpeptide, or used to detect antibodies specifically reactive with thehapten or peptide. Also contemplated are proteins for which antisera ormonoclonal antibodies are available, or nucleic acid molecules with asequence complementary to a target, a nanotag, a molecular mass bead, amagnetic agent, a nano- or micro-bead containing a fluorescent dye, aquantum dot, a quantum bead, a fluorescent protein, dendrimers with afluorescent label, a micro-transponder, an electron donor molecule ormolecular structure, or a light reflecting particle.

Additional labels contemplated for use with present invention include,but are not limited to, fluorescent dyes (e.g., fluoresceinisothiocyanate, Texas red, rhodamine, and the like), radiolabels (e.g.,³H, ¹²⁵I, ³⁵S, ¹⁴C, or ³²P), enzymes (e.g., horse radish peroxidase,alkaline phosphatase and others commonly used in an ELISA), andcolorimetric labels such as colloidal gold, colored glass or plasticbeads (e.g., polystyrene, polypropylene, latex, etc.), and luminescentor chemiluminescent labels (e.g., Europium (Eu), MSD Sulfo-Tag).

The label may be coupled directly or indirectly to the desired componentof the assay according to methods well known in the art. In a specificembodiment, the label is covalently bound to the component using anisocyanate or N-hydroxysuccinimide ester reagent for conjugation of anactive agent according to the invention. In one aspect of the invention,bifunctional isocyanate reagents are used to conjugate a label to abiopolymer to form a label biopolymer conjugate without an active agentattached thereto. The label biopolymer conjugate may be used as anintermediate for the synthesis of a labeled conjugate according to theinvention or may be used to detect the biopolymer conjugate. Asindicated above, a wide variety of labels can be used, with the choiceof label depending on sensitivity required, ease of conjugation with thedesired component of the assay, stability requirements, availableinstrumentation, and disposal provisions. Non-radioactive labels areoften attached by indirect means. Generally, a ligand molecule (e.g.,biotin) is covalently bound to the molecule. The ligand then binds toanother molecules (e.g., streptavidin) molecule, which is eitherinherently detectable or covalently bound to a signal system, such as adetectable enzyme, a fluorescent compound, or a chemiluminescentcompound.

The compounds useful in the method of the invention can also beconjugated directly to signal-generating compounds, e.g., by conjugationwith an enzyme or fluorophore. Enzymes suitable for use as labelsinclude, but are not limited to, hydrolases, particularly phosphatases,esterases and glycosidases, or oxidotases, particularly peroxidases.Fluorescent compounds suitable for use as labels include, but are notlimited to, those listed above as well as fluorescein derivatives,rhodamine and its derivatives, dansyl, umbelliferone, eosin,TRITC-amine, quinine, fluorescein W, acridine yellow, lissaminerhodamine, B sulfonyl chloride erythroscein, ruthenium (tris,bipyridinium), europium, Texas Red, nicotinamide adenine dinucleotide,flavin adenine dinucleotide, etc. Chemiluminescent compounds suitablefor use as labels include, but are not limited to, MSD Sulfa-TAG,Europium (Eu), Samarium (Sm), luciferin and2,3-dihydrophthalazinediones, e.g., luminol. For a review of variouslabeling or signal producing systems that can be used in the methods ofthe present invention, see U.S. Pat. No. 4,391,904.

Means for detecting labels are well known to those of skill in the artand are dictated by the type of label to be detected. Thus, for example,where the label is radioactive, means for detection include ascintillation counter (e.g., radioimmunoassay, scintillation proximityassay) (Pitas et al., Drug Metab Dispos. 34:906-12, 2006) orphotographic film, as in autoradiography. Where the label is afluorescent label, it may be detected by exciting the fluorochrome withthe appropriate wavelength of light and detecting the resultingfluorescence (e.g., ELISA, flow cytometry, or other methods known in theart). The fluorescence may be detected visually, by the use ofelectronic detectors such as charge coupled devices (CCDs) orphotomultipliers and the like. Similarly, enzymatic labels may bedetected by providing the appropriate substrates for the enzyme anddetecting the resulting reaction product. Colorimetric orchemiluminescent labels may be detected simply by observing the colorassociated with the label. Other labeling and detection systems suitablefor use in the methods of the present invention will be readily apparentto those of skill in the art. Such labeled modulators and ligands can beused in the diagnosis of a disease or health condition.

In another embodiment, the sample containing the plasma-derived proteinis first contacted with a binding agent (that is not a lectin protein)that binds the protein of interest. The binding agent may be anantibody, a soluble receptor, a ligand, a co-factor, or other proteinthat binds the plasma-derived protein or recombinant protein withspecificity. By “with specificity” is meant that the binding agent maybind a protein with particularity, but does not exclusively bind atarget molecule or moiety. “Specifically binds” refers to the ability ofa binding agent to recognize and preferentially binds to a definedtarget protein or other moiety (e.g. carbohydrate).

The method also optionally comprises a blocking step, wherein thebinding agent is contacted with a blocking agent prior to contactingwith the sample to remove any unwanted sugar moieties from the proteinbinding agent used to capture or bind the protein. Exemplary blockingagents, include but are not limited to, serum albumin, gelatin,glycosidase solutions, which cleave particular sugar residues,carbohydrate -modifying agents, such as acetylating agents ormethylating agents which modify the carbohydrates, a carbohydrateoxidizing solution, such as a periodate solution, and other blockingagents known in the art.

In one embodiment the labeled composition or the binding agent useful inthe methods of the invention is linked to a solid support, including butnot limited to, filters, plates or membranes. It is further contemplatedthat the labeled compounds and the binding agents may be labeled andinteract in solution. For example, the capture antibody may be labeledwith a fluorescent resonance energy transfer (FRET) donor molecule and asecond binding agent, such as a lectin protein, is labeled with a FRETacceptor molecule such that the molecules are in proximity when bindingoccurs. Alternatively, the lectin protein may be labeled with the FRETdonor and the protein molecule labeled with the FRET acceptor. Anotherpossibility is to separate quenching and fluorescent molecule bothpresent on the antibody or target when target and antibody hybridize.The molecules are only close enough for the label to emit if they areinteracting with the cognate reagent. This produces a system where themolecule only emits when it interacts with the reagent (directmonitoring). A narrow band pass filter can be used to block allwavelengths except that of the molecule's label. FRET molecule pairs arecommercially available in the art (e.g., from Invitrogen), and may beused according to the manufacturer's protocol. FRET emissions aredetected using optical imaging techniques, such as a CCD camera.

Another method of detecting lectin-plasma-derived protein interactionsis to label with an electron donor. This donor label would giveelectrons to an electrical contact to which the reagent is bound. See,for example, Ghindilis, A. (Biochem Soc Trans. 28:84-9, 2000) and Dai etal. (Cancer Detect Prey. 29:233-40, 2005) which describe enzymes usefulin and methods for electro immunoassays. The electron contact would thenbe read by an A to D (analog to digital) converter and quantified. Thehigher the electron count the more interactions took place.

One embodiment of a label capable of single molecule detection is theuse of plasmon-resonant particles (PRPs) as optical reporters, asdescribed in Schultz et al., Proc. Nat'l Acad. Sci., 97:996-1001 (2000),incorporated herein by reference. PRPs are metallic nanoparticles,typically 40-100 nm in diameter, which scatter light elastically withremarkable efficiency because of a collective resonance of theconduction electrons in the metal (i.e., the surface plasmon resonance).The magnitude, peak wavelength, and spectral bandwidth of the plasmonresonance associated with a nanoparticle are dependent on the particle'ssize, shape, and material composition, as well as the local environment.By influencing these parameters during preparation, PRPs can be formedthat have scattering peak anywhere in the visible range of the spectrum.For spherical PRPs, both the peak scattering wavelength and scatteringefficiency increase with larger radius, providing a means for producingdifferently colored labels. Populations of silver spheres, for example,can be reproducibly prepared for which the peak scattering wavelength iswithin a few nanometers of the targeted wavelength, by adjusting thefinal radius of the spheres during preparation. Because PRPs are bright,yet nanosized, they are used as indicators for single-moleculedetection; that is, the presence of a bound PRP in a field of view canindicate a single binding event.

Lectin:plasma-derived protein complexes are also detected usingnanoparticle-derived techniques. See, for example, Ao et al. (Anal Chem.78:1104-6, 2006) which describes gold nanoparticle quenching, Chen etal., (Biomaterials 27:2313-21, 2006) which describes SiO(2)/Aunanoparticle surfaces in antibody detection, and Lieu et al. (J ImmunolMethods. 307:34-40, 2005), which describes silicon dioxide nanoparticlescontaining dibromofluorescein for use in solid substrate-roomtemperature phosphorescence immunoassay (SS-RTP-IA).

For the methods of the invention, the binding agent or plasma-derivedprotein may be bound to a variety of solid supports, including but notlimited to filters, PVC membranes, PDVF membranes, PVC plates and otherplates which bind protein, microcarriers, macro solid phase beads,magnetic beads, made out of for example, polystyrene, nanoparticles,such as bimetallic silver-gold nanoparticles (Yan Cui et al., J. Phys.Chem. B, 110:4002-06, 2006), polyamide membrane (PAM) sheets (Sun et al,Analytical Letters 34:1627-37, 2001) and polysiloxane/polyvinyl alcoholbeads (Coêlho et al., Biotechnology Letters 24: 1705-1708, 2002).

For example, microspheres with multiple fluorescent molecular fillings,different materials, surface texture, surface patterns, etc. can beutilized as identification tags. It is contemplated that either thecapture antibody or the lysosomal enzyme is covalently bound to the beadand reacted against the opposite binding partner to assay the amount oflysosomal enzyme-specific antibody in serum. See, for example, CurrentProtocols in Immunology, Unit 6.11). Fluorescently filled microspheresare currently available from Molecular Probes, Inc. and other companies.Microspheres as small as 20 nm diameter polystyrene beads are currentlyavailable.

The plasma-derived protein or binding agent is attached to the solidsupport using standard protocols in the art, e.g., as described by themanufacturer of the support, or using standard chemical crosslinkingtechniques known in the art. See e.g., Pierce Biotechnology, Inc.(Rockford, Ill.) crosslinking kits.

Kits

Kits are also contemplated within the scope of the invention. A typicalkit can comprise lectin protein that specifically binds to aplasma-derived protein, such as a blood clotting factor, optionallylinked to a detectable label, and a protein standard containing a knownquantity of a protein. In one embodiment the kit further comprises abinding agent, which specifically binds the plasma-derived protein,wherein the binding agent is an antibody, a soluble receptor, a ligand,a cofactor (e.g., a second blood clotting factor or a chaperone protein)or another agent that specifically binds the plasma-derived protein. Thekit may optionally include reagents for carrying out an immunoassay suchas a second binding agent, linked to a detectable label that eitherbinds to a plasma-derived protein or to the lectin protein; if the labelis an enzyme, the kit may also include a substrate from which the enzymereleases a detectable signal. It is further contemplated that the kitcomprises a blocking agent in order to prevent non-specific binding ofthe lectin composition.

Additional aspects and details of the invention will be apparent fromthe following examples, which are intended to be illustrative ratherthan limiting.

EXAMPLES Example 1 Sambucus nigra Agglutinin (SNA) Binding of Plasma VWFand Recombinant CHO Cell-Derived VWF (rVWF)

Human proteins express unique glycosylation patterns compared toproteins produced in other organisms, which presents a difficulty whenproducing recombinant proteins where glycosylation is important inprotein function. One of the most popular cell lines for producingrecombinant human protein, Chinese hamster ovary (CHO) cells, lacks theenzyme α2,6 sialyltransferase, which confers addition of α2,6-sialicacid onto complex glycoproteins. While this difference may be minimalaffect with respect to interfering with activity of a protein, thisdifference in glycosylation can be used to distinguish recombinantlyproduced protein or naturally-produced secreted human proteins. Lectinproteins that distinguish between the different glycosylation patternscan be used in binding assays to determine the levels of recombinant ornaturally occurring protein in a biological sample. For example Sambucusnigra agglutinin (SNA) binds α2,6 linked neuraminic acid (sialic acid)but not α2,3 neuraminic acid.

To determine if SNA binding could distinguish naturally-occurring humanproteins from protein produced recombinantly in CHO cells, plasmaderived vWF (pVWF) and recombinantly produced vWF (rVWF) were used in anSNA binding assay.

An enzyme-linked immunosorbent assay (ELISA) is one method for detectingvon Willebrand factor antigen (vWF:Ag), which measures the quantity ofvWF, independent of vWF function, which usually constitutes vWFcomplexed with factor VIII. However, this assay cannot differentiatebetween plasma-derived or recombinant protein. Therefore, a modifiedform of this assay is used to detect glycosylated vWF.

Briefly, for the glycosylation detection assay, generally, a polyclonalor monoclonal anti-human VWF antibody preparation is bound topolystyrene microplates at slightly alkaline conditions. After blockingwith an inert non-glycosylated protein solution, incubation of thesamples with periodate oxidation reduces the ability of the coatingantibody to bind SNA by removing sialic acid residues on the antibodyprotein. Several dilutions of human plasma or a rVWF preparation arethen loaded to the wells. After a washing step removing non-bound samplecomponents the antibody-bound VWF/rVWF is allowed to react withbiotinylated SNA. The bound lectin (SNA) is then detected by reactionwith a streptavidin-peroxidase preparation measuring the peroxidaseactivity with an appropriate substrate.

The following experimental conditions were used to measure eitherplasma-derived vWF or rVWF carried out in separate assays: 100 μLcoating solution (anti-human VWF, (Dako, Denmark), diluted 1/500 incoating buffer 0.1 M Na₂CO₃, 0.1 M NaHCO₃, pH 9.5; alternatively anymonoclonal antibody can be used as well in an appropriate dilution) wasincubated for 16 hours at 4° C. or for 1 hr at 37° C. in wells of aMAXISORP™ F96 (NUNC, Germany) microplate. After washing in wash buffer(0.8% NaCl, 0.02% KCl, 0.02% KH₂PO₄, 0.126% Na₂HPO₄.2 H₂O, 0.05% Tween20 [EIA-grade, Bio-Rad, Hercules, Calif.], pH 7.0-7.4) the wells wereblocked by incubation with dilution buffer (0.1% gelatin [Bio-Rad,E[A-grade] or 0.1% bovine serum albumin [S[GMA, EIA-grade, St. Louis,Mo.], 2 mM benzamidine hydrochloride in washing buffer) using 200μL/well for 30 minutes at 37° C. After washing, periodate oxidation wascarried out by incubating the wells with 200 μL/well periodate solution(10 mM sodium periodate in 50 mM sodium acetate, pH 5.5) for 30 minutesat room temperature (RT). The washed plate as then incubated for 5minutes at RT with 200 μl/well ethanolamine solution (1% ethanolamine inwater) and washed again.

The sample dilutions were prepared using dilution buffer. For the humanplasma pool, a serial dilution series was prepared comprising thedilutions 1/400, 1/800, 1/1600, 1/3200 and 1/6400 corresponding toVWF:Ag concentrations ranging from 2.88 to 0.18 mU VWF:Ag/mL. For thesamples containing rVWF, the rVWF preparation was used at highconcentrations (311-19 mU/mL). 100 μL/well were loaded in duplicates tothe wells and incubated for 60 minutes at RT. The plate was then washedand 100 μL/well of biotinylated SNA (Vector Laboratories, Burlingame,Calif.) was added at a concentration of 2 μg/mL. The plates wereincubated for 60 minutes at RT and washed, and 100 μl/wellstreptavidin-peroxidase (Dako, diluted 1/4000) was added and incubatedfor 30 minutes at RT. The incubation was terminated by a washing step.Bound peroxidase was detected by a color reaction with the peroxidasesubstrate SUREBLUE™ (KPL, Gaithersburg, Md.). 100 μL/well of sample wasincubated for 10 to 15 minutes at RT. The reaction was stopped by adding100 μL/well 1.5 M H₂SO₄. Subsequently, the plate was measured with anELISA reader at 450 nm with the reference wavelength set to 620 nm. Forfurther data evaluation, a linear regression analysis was performedusing the blank corrected mean values of the optical densities measuredand the VWF:Ag concentrations of the dilutions of the plasma pool. Thecalibration curve obtained is used to calculate the SNA binding ofunknowns relative to that obtained for the plasma pool, which was set at100%.

The analysis of plasma VWF resulted in a clear dose dependent relationbetween the VWF:Ag concentration and the SNA-binding measured. Thisrelation was highly linear (R²=0.9996) within the defined range of 0.2to 2.9 mU VWF:Ag/ml allowing the construction of a linear calibrationcurve. In contrast to plasma VWF, CHO cell-derived rVWF showed nobinding to SNA even when 100 times higher concentrations were used.Thus, the preparations can be differentiated by their differentreactivity with SNA. Similar results were obtained using a monoclonalanti-human VWF with a defined binding epitope in the Al domain of humanVWF. These differences in reactivity towards SNA reflect the fact thatCHO cell-derived rVWF contains no α2,6-linked neuraminic acid, which isthe glycan structure specifically required for binding to SNA.

Example 2 SNA Binding of Plasma Factor IX (pFIX) and RecombinantCHO-Cell Derived Factor IX (rFIX)

In order to determine if the reactivity of the plasma-derived VWF:Agwith SNA is unique to the plasma VWF, a second CHO-derived bloodclotting factor, Factor IX (FIX), was analyzed in an SNA binding assay.

A polyclonal anti-human FIX antibody preparation was bound topolystyrene microplates as above. For the human plasma pool, a geometricdilution series was prepared in dilution buffer using the dilutions1/320, 1/640, 1/1280, 1/2560 and 1/5120 corresponding to FIX:Agconcentrations ranging from 3.09 to 0.19 mU FIX:Ag/mL. The rFIXpreparation was investigated at higher concentrations (78-4.9 mU/mL).100 μL/well were loaded to the wells in duplicates and incubated for 60minutes at RT, and development carried out as described previously.

Similar to the results with the plasma VWF protein, there was a cleardose dependent relation between the plasma FIX:Ag concentration and theSNA binding measured. This relation was linear (R²=0.9963) within thedefined range of 0.2 to 3.1 mU FIX:Ag/ml allowing the construction of acalibration curve. In contrast to plasma FIX, CHO-cell derived rFIXshowed no binding to SNA even at the 10 times higher concentrationsinvestigated. Thus, both preparations can be differentiated by theirdifferent reactivity with SNA.

Example 3 Measurement of SNA Binding of Plasma VWF and CHO Cell-DerivedrVWF After Neuraminidase Treatment

To ensure that the binding to SNA was specific for SNA, the specificityof the binding to SNA was investigated using the enzyme neuraminidase,which cleaves off or desialylates both α2,6 and α2,3 neuraminic acidfrom oligosaccharides. After incubating antibody-bound plasma VWF andrVWF with increasing levels of neuraminidase on the microtiter plate,the effects of neuraminidase desialylation on the SNA binding of pVWFand rVWF were measured.

The anti-VWF microtiter plates were prepared for analysis as describedpreviously. Both the human plasma pool and the rVWF preparation werediluted to obtain VWF:Ag concentrations of 5 mU/mL and 2.5 mU/mL. 100μL/well of these dilutions were loaded to the coated, periodate-oxidizedplates and incubated for 60 minute at RT and washed afterwards. Theneuraminidase digest was then carried out on the plate with theplasma-derived vWF and rVWF immobilized by the bound antibody.Neuraminidase (Sigma, St. Louis, Mo.) was used at the concentrations of0, 1, 5, 10 and 20 mU/mL, obtained by diluting the enzyme with 20 mMBis-Tris-Propane containing 2 mg/mL bovine serum albumin. 100 μL/wellneuraminidase solution was incubated for 2 hours at 37° C. Afterwards,the plates were washed and incubated with biotinylated SNA (Vector; 2μg/mL; 100 μL/well) for 60 minutes at RT. This incubation was terminatedby washing before the plates were incubated 30 minutes at RT withstreptavidin peroxidase (Dako, 1/4000). After a final washing step, thebound peroxidase activity was measured with the peroxidase substrateSUREBLUE™ as above.

Results show that, whereas CHO-cell derived VWF shows no binding to SNAin the SNA assay, this binding is not altered after treatment withneuraminidase, however, the SNA binding of plasma VWF is reducedproportional to the concentration of the neuraminidase applied. Thisresult was observed with both VWF:Ag concentrations investigated. At aneuraminidase concentration of 20 mU/mL and under the experimentalconditions applied, the SNA binding is less than 95% of the initiallymeasured concentration.

These results showed that the SNA protein specifically bound to α2,6N-acetylneuraminic acid, since removal of neuraminic acid from theplasma-derived protein caused loss of binding. CHO cell derived rVWFshowed no binding to SNA with and without neuraminidase treatmentbecause the neuraminic acid is present only in a linkage which is notrecognized by SNA or hydrolyzed with neuraminidase.

Example 4 Measurement of Binding of Plasma VWF and CHO Cell-Derived rVWFAfter Neuraminidase Treatment to the Lectin Maackia amurensis Agglutinin(MAA)

Because rVWF does not bind SNA due to the lack of α2,6-linked neuraminicacid, removing neuraminic acid was not expected to alter binding of SNAto rVWF. In order to confirm that the recombinant protein did expresssialic acid moieties, but in a different configuration than the plasmaderived sialic acid, a binding assay that measures binding of protein toα2,3-linked neuraminic acid is used to detect the recombinantlyexpressed α2,3-linked neuraminic acid on the recombinant protein. Thelectin, Maackia amurensis agglutinin (MAA), which binds α2,3-linkedneuraminic acid, was used to determine if desialylation of rVWF occurredin the presence of neuraminidase. After incubating antibody-bound plasmaVWF and rVWF with increasing levels of neuraminidase, the binding of theproteins to MAA was measured.

Anti-vWF plates were prepared as above. Both the human plasma pool andthe rVWF preparation were diluted to obtain VWF:Ag concentrations of 5mU/mL and 2.5 mU/mL. 100 μL/well of the sample dilutions were loaded tothe coated, periodate-oxidized plates and incubated for 60 minutes at RTand washed afterwards. The neuraminidase digest was then carried out onthe plate. Neuraminidase (Sigma) was used at the concentrations of 0, 1,5, 10 and 20 mU/mL. Afterwards, the plates were washed and incubatedwith the biotinylated MAA (Vector, 1 μg/mL) for 60 minutes at RT. Theincubation was terminated by washing, after which the plates wereincubated 30 minutes at RT with streptavidin peroxidase (DakoCytomation,1/4000). After a final washing step, the bound peroxidase was measuredas previously described.

Recombinant vWF was bound by the MAA lectin indicating the presence ofsialic acid on the recombinant protein. Addition of neuraminidase to theculture wells abolished both the plasma VWF and the rVWF binding to MAL,which recognizes neuraminic acid when present in α2,3-linkage. Even thelowest enzyme concentration tested showed a reduction of >95% of the MALbinding. Similar data were obtained when VVVF was used at aconcentration of 2.5 mU/mL. Thus, effective desialylation also occurredfor the rVWF preparation detectable only when using MAL, butundetectable when SNA is applied indicating the specificity of SNAbinding to plasma VWF and not recombinant VWF.

Example 5 Inhibition of the SNA Binding to Plasma VWF and CHOCell-Derived Recombinant VWF (rVWF) with 6′-Sialyllactose

Lectins bind specifically to monosaccharides or oligosaccharides, whichcan either be free in solution or as part of larger oligosaccharidesfound on glycoproteins, glycolipids or other glycoconjugates. Thespecificity of the lectin binding can be investigated by inhibitionstudies using these mono- or oligosaccharides in competition bindingassays. The trisaccharide 6′-sialyllactose is known to be a potentinhibitor of the binding of the lectin SNA and was used to confirm thespecificity of the binding of SNA to plasma VWF.

Anti-vWF plates were coated and prepared as above. The human plasma poolsamples were diluted to obtain a VWF:Ag concentration of 5 mU/mL. 100μL/well was loaded and incubated for 60 minutes at RT. 50 μL 6-sialylactose (Sigma, A-9204) was added to the plate at concentration rangingfrom 2.1 to 150 μM and then 50 μL of the biotinylated SNA (Vector, 1μg/mL) was added and incubated for 60 minutes at RT. The incubation wasterminated by washing, after which the plates were incubated 30 minutesat RT with streptavidin peroxidase (DakoCytomation, 1/4000). After afinal washing step, the hound peroxidase was measured as previouslydescribed.

The trisaccharide 6′-sialyllactose showed concentration-dependentinhibition of the binding of SNA to plasma VWF under the experimentalconditions used, demonstrating approximately 25% inhibition at 10 μM6′-sialyllactose and 75% inhibition at 100 μM 6′-sialyllactose. Thisobservation confirmed that the measured binding was dependent on theN-glycan structures of plasma VWF and was not caused by any otherreaction.

Example 6 Inhibition of the SNA Binding to Plasma VWF and CHOCell-Derived Recombinant VWF (rVWF) with 3′-Sialyllactose

Another trisaccharide, 3′-sialyllactose, in which the neuraminic acid islinked α2,3 to the galactose residue of the lactose, would be expectedto show no effects on the binding of SNA to plasma VWF since plasma VWFlacks α2,3 sialic acid. To examine the specificity of binding, theeffects of 3′-sialyllactose on plasma-derived protein and CHO-derivedrecombinant protein was measured.

VWF-Ag specific plates were prepared as above and the 3′siallylactoseinhibition assay performed as described for the 6′ sialyllactose assayin Example 5 above. Results demonstrated that 3′-sialyllactose had noeffect on the binding of SNA to plasma VWF, confirming that SNA binds toneuraminic acid only when present in α2,6-linkage.

Example 7 4-Point Calibration Curve for the Measurement of CHOCell-Derived Recombinant VWF (rVWF) in the Presence of Plasma VWF

In order to determine if the SNA binding assay could allow quantitationof the amount of plasma derived protein compared to recombinant proteinin a single sample, test samples comprising both the plasma VWF andrecombinant VWF were analyzed for SNA binding and a calibration curvedeveloped for quantitation of rVWF in the samples.

Briefly, a human normal plasma pool containing VWF:Ag at a concentrationof approximately 1 U/mL was spiked with 0, 02, 0.5, 1.0 and 2.0 U rVWF.The VWF:Ag concentration and the SNA binding of these samples wasmeasured in six independent test units. The SNA binding measured for aseparate, non-spiked human plasma pool was used as basis to calculate anexpected, hypothetical SNA binding for the spiked samples under theassumption that the VWF:Ag present in these samples would be plasma VWFonly. The difference between these hypothetically calculated SNA bindingvalues and the measured values was calculated, which reflects theamounts of rVWF in mixture with the plasma VWF. To verify thisassumption, the differences in binding were then plotted against theamount of rVWF contained in these samples and a linear regressionanalysis was performed. Thus, a calibration curve was obtained allowingfor determination of the concentrations of rVWF in the presence ofplasma VWF.

The anti-vWF microtiter plates were prepared as above. For thecalibration curve, a sample dilution series comprising the dilutions1/100, 1/200, 1/400, 1/800 and 1/1600 was prepared using a human plasmapool. Samples were diluted to obtain VWF:Ag concentrations within therange covered by this calibration curve. 100 μL/well of these dilutionswere loaded, incubated for 15 minutes at RT before 100 μl/well of thedetection antibody (rabbit anti-human VWF-peroxidase, Dako, 1/2000) wasadded. This incubation was carried out for 60 minutes at RT andterminated by washing. The bound peroxidase activity was measured withSUREBLUE™ peroxidase substrate. The color reaction was stopped using 1.5M sulfuric acid. The plates were measured subsequently with an ELISAreader at 450 nm with the reference wavelength set at 650 rim. TheVWF:Ag concentration of these samples was then obtained in U/mL afterextrapolation on the calibration curve.

The SNA binding of the samples was measured using anti-vWF platesprepared as above. The sample dilutions were prepared using dilutionbuffer. For the calibration curve a dilution series comprising thedilutions 1/400, 1/800, 1/1600, 1/3200 and 1/6400 was prepared using ahuman plasma pool. Samples were diluted to obtain SNA binding within theconcentration range covered by this calibration curve. 100 μL/well ofeach dilution was loaded to the coated, periodate-oxidized plates andincubated for 60 minutes at RT. Afterwards, the plates were washed andincubated with biotinylated SNA, and SNA binding measured as previouslydescribed.

Table 1 shows data obtained in the six independent test units for theVWF:Ag concentration and the SNA binding of these samples.

TABLE 1 VWF:Ag and SNA binding of spiked samples CHO-cell derived rVWFspiked to human plasma 0 U 0.2 U 0.5 U 1.0 U 2.0 U VWF:Ag Test 1 0.931.11 1.49 2.07 3.18 Test 2 0.94 1.11 1.47 1.95 3.21 Test 3 0.91 0.991.26 1.93 2.98 Test 4 0.92 1.06 1.32 1.99 3.14 Test 5 0.88 1.05 1.291.92 3.06 Test 6 0.91 1.08 1.30 1.56 3.50 Mean 0.92 1.07 1.36 1.90 3.18SD 2.3 4.2 7.3 9.3 5.6 SNA binding Test 1 130.1 99.0 81.1 52.4 34.5 Test2 125.3 105.2 76.6 56.7 33.1 Test 3 135.0 119.8 104.3 62.5 37.2 Test 4135.4 111.1 87.0 63.0 38.3 Test 5 152.0 98.1 87.9 54.2 33.0 Test 6 145.3107.6 91.7 73.4 34.0 Mean 137.2 106.8 88.1 60.4 35.0 SD 7.2 7.6 10.912.8 6.3

The SNA binding of the samples was obtained after extrapolation from aSNA:protein binding calibration curve and levels are expressed relativeto that of the human plasma pool which was not spiked with recombinantprotein, defined as 100% SNA binding. Plasma VWF at mean concentrationof 0.92 U had a mean SNA binding corresponding to 137.2% of thatmeasured for a human plasma pool. Using this mean SNA binding asmeasured for the human plasma sample containing no rVWF, thehypothetical SNA binding was calculated for the spiked samples under theassumption that the VWF:Ag measured was only plasma VWF. Results areshown in Table 2.

TABLE 2 Calculation of the hypothetical SNA binding for the plasmasamples spiked with rVWF CHO cell-derived rVWF spiked to human plasma 00.2 0.5 1.0 2.0 Total VWF 0.92 1.07 1.36 1.90 3.18 rVWF — 0.15 0.44 0.992.26 SNA binding expected 137.2 159.9 203.2 285.4 476.6 SNA bindingmeasured 137.2 106.8 88.1 60.4 35.0 Difference 0.0 53.1 115.1 225.0441.6 SD 4.0 12.5 28.7 28.0

The difference between the calculated binding and the expected SNAbinding correlated well with the concentrations of CHO cell derived rVWFspiked into the human plasma samples within the range investigated inthis experiment. A good linear relationship was observed, when 0.2 to2.0 U rVWF were added to a sample already containing 1 U VWF:Ag, whereinincreasing concentrations of recombinant vWF in the sample resulted inlarger differences in expected binding. A plot of the calibration curvecorrelating the difference in SNA binding with the amount of recombinantprotein is shown in FIG. 1. These results show that the assay provides areliable method for differentiating between plasma-derived andrecombinant protein in a sample and determining the levels of each typeof protein in a single sample.

Example 8 8-Point Calibration Curve for the Measurement of CHOCell-Derived Recombinant VWF (rVWF) in the Presence of Plasma VWF

An additional quantitative assay was developed for increased sensitivityin measuring the amount of plasma derived protein and recombinantprotein in a sample.

A human normal plasma pool containing VWF:Ag at a concentration ofapproximately 1 U/mL was spiked with 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0,1.2 and 1.5 U rVWF. The VWF:Ag concentration and the SNA binding ofthese samples was measured in six independent test units. The SNAbinding measured for the non-spiked human plasma pool was used as basisto calculate an expected, hypothetical SNA binding for the spikedsamples as in Example 7.

The VWF-specific plates were prepared as above. For the calibrationcurve, a dilution series comprising the dilutions 1/100, 1/200, 1/400,1/800 and 1/1600 was prepared using a human plasma pool, and the VWF:Agconcentration and SNA binding measured as in Example 7. The SNA bindingof the samples was obtained after extrapolation on the calibration curveand levels are expressed relative to that of the human plasma pool,defined as 100% SNA binding. Table 3 shows the measuring data obtainedin the six independent test units for the VWF:Ag concentration and theSNA binding of these samples.

TABLE 3 VWF:Ag and SNA binding of spiked samples VWF: CHO cell-derivedrVWF spiked to human plasma Ag 0 0.2 U 0.4 U 0.5 U 0.6 U 0.8 U 1.0 U 1.2U 1.5 Test 1 0.85 1.10 1.27 1.35 1.39 1.70 1.90 2.00 2.20 Test 2 1.091.10 1.24 1.32 1.47 1.94 2.24 — — Test 3 0.95 1.06 1.22 1.34 1.39 1.801.89 2.06 2.15 Test 4 0.95 1.09 1.20 1.38 1.43 1.62 1.89 2.00 2.07 Test5 0.95 1.13 1.22 1.42 1.49 1.68 1.85 1.95 2.09 Test 6 0.96 1.16 1.401.38 1.48 1.62 1.81 2.04 2.13 Mean 0.96 1.11 1.26 1.37 1.44 1.73 1.932.01 2.13 RSD 8.0 3.1 5.8 2.6 3.1 7.2 8.1 2.1 2.4 CHO cell-derived rVWFspiked to human plasma SNA 0 0.2 U 0.4 U 0.5 U 0.6 U 0.8 U 1.0 U 1.2 U1.5 Test 1 134.6 94.3 80.2 76.4 71.5 62.9 60.8 55.0 56.3 Test 2 110.090.0 81.6 73.7 74.8 n.d. n.d. 43.0 42.6 Test 3 135.1 92.7 85.7 77.5 73.459.8 55.6 56.4 56.0 Test 4 117.1 90.3 87.8 85.2 76.7 58.8 n.d. 56.0 50.6Test 5 113.8 90.7 82.0 76.1 71.9 60.6 53.1 50.6 46.6 Test 6 130.6 96.083.4 85.0 91.1 70.8 67.6 54.5 53.2 Mean 123.5 92.3 83.5 78.9 76.6 62.659.3 52.6 50.9 RSD 9.1 2.6 3.4 6.2 9.6 7.7 10.8 9.8 10.7

Plasma VWF at a concentration of 0.96 U had a mean SNA bindingcorresponding to 123.5% of that measured for a reference plasma pool.Using this mean SNA binding measured for the human plasma samplecontaining no CHO-cell derived rVWF, the hypothetical SNA binding wascalculated for the spiked samples under the assumption that the VWF:Agmeasured was only plasma VWF. These data are shown in Table 4.

TABLE 4 Calculation of the hypothetical SNA binding for the plasmasamples spiked with CHO cell-derived rVWF CHO cell-derived rVWF spikedto human plasma 0 0.2 0.4 0.5 0.6 0.8 1 1.2 1.5 Total VWF 0.96 1.11 1.261.37 1.44 1.73 1.93 2.01 2.13 rVWF 0.15 0.30 0.41 0.48 0.77 0.97 1.051.17 SNA binding expected 123.5 142.6 162.2 175.9 185.8 222.5 248.7259.0 274.2 SNA binding found 123.5 92.3 83.5 79.0 76.6 62.6 59.3 52.650.9 Difference 0.0 50.3 78.7 96.9 109.2 159.9 189.4 206.4 223.4 SD n.d.1.3 2.7 6.0 10.5 12.4 20.5 20.1 23.9

Similar to the 4-point calibration assay described above, the differenceto the expected SNA binding correlated well with the concentrations ofCHO cell-derived rVWF spiked to human plasma even when 8 concentrationsin a narrower spiking range where investigated. A plot of the 8-pointcalibration curve correlating the difference in SNA binding with theamount of recombinant protein is shown in FIG. 2.

These results show that the amount of recombinant protein in a sample ofhuman plasma can readily be differentiated from naturally-producedprotein in the sample, based on the differential expression ofcarbohydrate moieties. This type of assay is useful in the clinicalsetting to determine the amount of exogenous/therapeutic protein beingadministered and its penetration into the blood stream compared to theamount of naturally-produced protein. This assay is also useful tocompare the efficacy of one therapeutic to another by comparing serumhalf-life in viva

Numerous modifications and variations in the invention as set forth inthe above illustrative examples are expected to occur to those skilledin the art. Consequently only such limitations as appear in the appendedclaims should be placed on the invention.

1-18. (canceled)
 19. A method to differentiate plasma-derived proteinand recombinant protein in a sample comprising, contacting the samplewith a composition comprising a lectin protein; detecting binding of thelectin to the protein; and comparing the amount of binding ofprotein-bound lectin in the sample to a lectin:protein binding curve todetermine the amount of plasma-derived protein in the sample.
 20. Themethod of claim 18 wherein the lectin is Sambucus nigra agglutinin(SNA).
 21. A kit for quantitating levels of plasma derived protein andrecombinant protein in a sample, wherein the plasma-derived protein andthe recombinant protein encode the same protein, the kit comprising aprotein binding agent; a composition comprising a lectin specific for acarbohydrate on the plasma-derived protein and a detectable label; and aprotein standard.
 22. The kit of claim 21 wherein the binding agent isan antibody.
 23. The kit of claim 22 wherein the antibody is amonoclonal antibody.
 24. The kit of claim 21 wherein the lectin isSambucus nigra agglutinin (SNA).
 25. The kit of claim 21 wherein thedetectable label is biotin.
 26. The kit of claim 21 optionallycomprising a blocking reagent.
 27. The kit of claim 26 wherein theblocking agent is a periodate solution.
 28. The kit of claim 21 whereinthe protein is a blood clotting factor.
 29. The kit of claim 28 whereinthe blood clotting factor is selected from the group consisting of vonWillebrand factor, Factor VIII, Factor VII, and Factor IX.